Method of and means for varying radio frequency currents



' Dec. 18, 1934. M. OSNOS 1,985,104

METHOD OF AND MEANS FOR VARYING RADIO FREQUENCY CURRENTS Filed June 14, 1929 INVENTOR MENDEL ATTORNEY or variation inthe wave-length is sufficient to Patented Dec. 18, 1934- VARYING. p

. RADIO FREQUENCY QURBENTS I Germany "Application June 14', 1929,-Serial No; 370,826

' In Germany June 25, 1?,28 I

It isknown from practice that radio trans- ,mission on very shortwaves is often attended by what isknownas fading. It has often been observed that occasionallya very slight change insure satisfactory communication. With this end in view the suggestion has been made to alter the frequency of the outgoing wave periodically, say, several thousand times per second,

with'the result that part of. the energy which, happens to be at the frequency most favorable 1 at the time during. such alterations in wavelength ,will reach the receiving station at the rhythmof such alternatingcurrent, in a manner free from fading, so that telephonic or telegraphic communication is made possible. This rhythm variation in the wave-length artificially produced in the said manner is known as wobblingyn However, a technical difliculty arises insofar as the requisite slight change in the wave- 'len'gthor frequency. during wobbling must be exactly maintained. within definite limits.

Now, in the present invention ways and means are disclosed whereby wobbling or'frequency variation iseffected in a simple manner and with I suflicientaccuracy for the elimination of fading.

The schememay also be used to good advantage in'systems utilizing frequency modulation.

The underlying idea of the invention consists.

in that'in the circuit which controls the frequency of the tube to be controlled (say, in its grid circuit), one or more crystals are combined with one or more tubes whose impedance is altered at the rhythm or rate of the desired wobbling frequency by the aid of a suitable auxiliary alternating potential.

A number of embodiments of the basic idea of the invention are diagrammatically shown by way of example in Figures 1 to 7 of the accompanying drawing.

Referring to Figure 1, a is the tube to be controlled, Z and r denote the inductances and ohmic resistances connected between its filament f and its grid 9. k is a grid crystal, and w an impedance, inductive, or capacitive in series with said crystal. In parallel relation with said resistance is a thermionic tube b either with or without a grid. Through an inductance L which offers a high impedance forthe radio frequency current of tube g or of its grid circuit, the tube b is sup-' causes, at the rhythm of the same frequency, corresponding changes in the gridfrequency of tube g, and in this manner the desired wobbling is produced. v

In the scheme shown crystal k1 is connected in parallel to' crystal is. It is not absolutely necessary to provide a parallel impedance :1: in case. But it is suitable to so choose crystals k and R1 that their natural waves will differ slightly from' each other. This scheme offers the advantage that the amplitude of the radio frequency waves generated by tube a maybe kept substantially constant in spite of thefrequency changes occasioned by wobbling.

In the circuit arrangement'hereinbefore described, only every other half-wave of potential 6 is used for wobbling (control), owing to the unilateral action of valve tube b. In order to utilize both halves of the wave of potential e, the variable tube resistance acted upon by potential 6 may consist of two oppositely connected tubes b and b1, as shown in Figure 3; One half of potential e acts upon the resistance of tube b and the next half influences the resistance-of tube b1.

' While the auxiliary potential e is still low, the two tubes b andbl act as stoppers, and the oscillation frequency of tubea orits grid circuit is substantially determined and governed by crystal 701. But when potential e "during either half of the cycle exceeds a definite value, then eithertube b or tube bl will become permeable for the current, according to the direction of potential e, and crystal It becomes operative, so that during these intervals of time the radio frequency of the tube a is governed by the two crystals k and A similar circuit scheme adapted to utilize both half-waves of the control potential e is shown in Figure 4. Also in this instance, the two tubes b, b1, are connected in opposition. The control potential e is suppliedby way of the primary winding of a transformer t whose secondary is includedbctween the cathode of tube b and the anode of tube b1, its middle being connected with the grid circuit of tube a or if desired, with the grounding terminal.

If also the branch of the second crystal k1 is to be directly controlled by a tube resistance, arrangements, for instance, could be chosen in a way as illustrated in Figure 5. Also here the two tube resistances subjected to the control by the auxiliary alternatingcurrent potential e are disin Figure 2, a second I 53 i A T bFFl-CE bling frequency, while impermeable for the radio impedances controlling them must be connected in parallel thereto as shown, e. g., in Figure 6, instead of being connected in series'there'with as in the preceding embodiment. The crystal belonging to a given tube will then be disconnected:

or be cut in circuit, according to whether the respective tube is permeable orimpermeable for the current.

If the tubes b and bl comprised in all of the circuit schemes hereinbefore describedare furnished with grids, then the auxiliary potential e provided to influence their resistance could be applied also to the grid instead of to the plate. In thisinstance, an arrangement as illustrated, for instance, in Figure 3, would have to be modified to result in a scheme of the kind illustrated in Figure 7, or else the two tubes 1) and bl could be connected in the same sense, while the direction of coupling of the grid, transformer in onev of these tubes would have to be'reversed.

I claim as my invention:

1. Means for producing oscillations of a constant amplitude and of a frequency which varies between fixed limits comprising, a thermionic oscillation generator having input electrodes, a frequency determining circuit comprising parallelly connected crystals connected between said input electrodes, a variable impedance in series with each of said crystals, and means for varying said impedance oppositely and continuously at a super-audible rate.

2. Means for producing oscillations of a constant amplitude and of a frequency which varies between fixed limits comprising, a thermionic oscillation generator having input electrodes, a plurality of crystals of different frequencies connected between said input electrodes, circuits for connecting the internal impedance of a separate thermionic device with each of said crystals, and means for varying alternately the conductivity of said thermionic devices. I

3. An oscillation generator comprising, a thermionic tube having, input electrodes, aplurality of crystals of different frequencies, each having a terminal connected to one of said input electrodes, a plurality of thermionic discharge devices, means for connecting opposed terminals of said devices together and to the other of said input electrodes, means for connecting the. free terminals of each of said thermionic discharge devices to the other electrode of a different one of said crystals, and means for applying alternating current potentials continuously to the electrodes in saidthermionic discharge devices.

- 4'. In combination, an electron discharge device oscillator having a control electrode and cathode, said oscillator being adapted to produce oscillations, and means for determining the frequency of the oscillations produced and for shifting the same between two frequencies as a limit comprising, a pair of piezo-electric crystals, one of said crystals having a frequency equal to the frequency of'the upper limit of said frequencies between which the oscillations are to be shifted,.the other of said crystals having a frequency equal to the frequency of the lower limit between which said oscillationsv are to be shifted, a circuit connecting one terminal of each of said crystals to the con-- trolgrid of said device, unilateral impedances connecting the other terminals of sai'd'crystals to the cathode of said device, said impedances being of opposed polarity, and means for varying the values of said impedances alternately to thereby shift the control of said oscillations from one of said crystals to the other, thereby'shifting the frequency of the oscillations produced.

5. An oscillation generator comprising, a thermionic tube having a control grid and a cathode, a plurality of piezo-electric crystals of different natural frequencies, each crystal having two electrodes, a connection between one electrode of each crystal and said control grid, an additional thermionic tube having two electrodes, a connection between the other electrode of one of said crystals and one electrode of said additional tube, a connection between the other electrode of said additional 'tube and the cathode of said first named tube, a connection between the'oth'er electrode of the other of said crystals and the oathode of said first named tube, and means forv varying the impedance between the electrodes of said additional tube at a modulating frequency rate.

MENDEL OSNOS. 

